Project Update August 20th 2015: This forum post update covers much of the work we did from late May through mid June of 2015 on our customer's tube framed 69 Camaro "Pro Touring" track car. A little more deconstruction was needed, but for the most part that was all wrapped up and the real fabrication work really got underway in this period.

Before we get started I wanted to list the forums we're posting this build thread on. Note: The pictures in all of my build threads can be clicked for higher rez images or sometimes videos, but for some reason clickable images do NOT work over at S197forums.

One of these I own (vorshlag), two of them I sponsor (sccaforums + S197forums), and corner carvers puts up with my shenanigans (mostly). Later in 2015 a moderator from Lateral-G asked me to share it there, too. If there's another forum that would welcome this build thread (even with...gasp... watermarked pictures), and it has approval from an admin or moderator to post as-is, please PM me and I can port it over. Not that this is a ground breaking build or some unknown tech going into it, but its a fun Pro Touring / track build that not a lot of shops are willing to share the behind the scenes work on, to this level.

New Rear Suspension + Frame Section = Thoughts About IRS?

Once we had the new '69 Camaro frame rails laid out on the "frame table" we started looking at the rear suspension. It came here with a custom 9" Ford axle with a semi-finished 3-link (fore-aft control arms) and a Watts Link (lateral location), but it didn't look right. Sure enough, after Ryan measured the arm lengths, pickup points, and positions, then input the numbers into 3D suspension software, the the geometry was "less than ideal" for track use.

So by now we knew we would be massively changing everything out back - adding all new rear frame rails, altering the geometry and mounting points on the rear control arms, and making a new Watts using some of the old parts. And the solid axle housing was bare - it had no differential or axles installed. So a thought occurred to me... would now be a good time to discuss an Independent Rear Suspension?

We proposed both a C5/C6 rear transaxle and rear subframe/suspension for the 69 Camaro IRS

We pitched the idea to the customer, first showing him a C5/C6 rear transaxle and suspension, using the OEM aluminum rear cradle, arms, halfshafts, and transaxle. But he was invested in the custom ford 9" axle that was already in the build and didn't want to give that up. Plus after we measured a C5 in the shop we realized that an unmodified C5/C6 rear subframe and halfshafts would push the track width wider by at least 4 inches, which meant rear flares, and that would disrupt the original bodylines too much.

Custom IRS we built for a 99 Miata with an LS V8 swap = costly + time consuming

There are some aftermarket rear IRS setups but they aren't very.... good. Sorry, they are generally "Not appropriate for this application" - again, with massive Hoosiers making big grip numbers, and serious track performance as the end goal. So doing a completely scratch built IRS was an option, and we've done that before (on the Miata, above) but it would be a lot of custom work and added costs. We discussed the pros and cons with the customer and in the end we scrubbed the IRS idea, as this build was already too far along and LOTS more perfectly good parts would get chucked. So we got back on track and started diving into the new rear suspension geometry and frame rails.

Getting The New Frame Started

As I mentioned at the end of my last entry, the center of the chassis was built from 2x4" tubular frame sections, which were first fitted into the gutted unibody tub. These were then transferred to our frame table at the same width.

The existing aftermarket front suspension was added at the right location and tubing was made to joint the "center" to the "front" frame sections. We don't know where this front frame clip came from, but it doesn't really matter. There are dozens of "bolt in" front suspensions for the 1st gen F-bodies and they span back over a decade, with lots of revisions along the way.

We had some serious reservations about some of the material used in the major suspension mounting point load paths, but the customer really wanted to use what he had. So we moved forward and mounted it to the frame table at the correct height, so we could do more mock-up and measurements.

Two things became obvious once it was joined to the center section and tack welded together. First, the maximum amount of negative camber we could get with this setup was -1.0° up front. Which is nowhere near enough, as these Hoosiers would probably generate enough cornering power to need closer to -2.5 to -3.5° up front. So we'd have to cut off the main upper control arm mounting plates, move them inboard, and figure out how to reinforce those plates to counter cornering loads.

Second, there were some surprising side-to-side suspension geometry inconsistencies in the lower control arm brackets of this production built front clip. These were going to already have be heavily modified and beefed up anyway, but its just odd that supposedly CNC laser-cut brackets could be assembled and be off by 5/8" from side to side. Again, we don't know who originally built this subframe kit, or if it was modified after it was installed, but it was a big hot mess.

So we now knew we had to remove the upper mounting plates and move them for more negative camber travel, then reinforce the flimsy plates heavily. Not to mention all of the control arm pick-up points were thin, poorly supported steel plate - everything needed to be heavily beefed up. The geometry wasn't good, the alignment capability was poor, and the engineering wasn't up the grip levels planned for this car.

In the end, it was easier to just build a whole new front subframe than "fix" was was here. Ryan did all of the geometry calcs in the 3D software and came up with a new front frame rail width and placement so that the suspension loads would go through the frame members directly or through plate and tubing added to the 2x4" rails. When we displayed all of the shortcomings of the old front subframe, our customer agreed. Now the complete front subframe can be sold to someone else - to use on a street rod or drag car, which this design (above) is more appropriate for.

Updated Rear Suspension and Frame

So we now are tasked to make the entire frame from scratch. We ordered the pre-bent rear 2x3" rectangular rear frame rail sections below to work with a solid axle rear suspension. Being originally made for drag cars with long lower arms, they were just a bit too long to fit the confines of the chassis we had laid out, so they needed to be shortened several inches...

This isn't particularly difficult, just a little time consuming to do right. First the rails are cut to the correct length, then a "slug" of tubular steel is made that fits inside the junction. Drilled holes in the 2x3" sections allow for rosette welds and of course a weld at the main junction. Then it is lightly ground for aesthetics. This makes the welded frame section stronger at the joint than before, with just a little more weight.

All of that work was still MUCH easier than hand making these curved frame sections that go over the solid axle. Pie-cut pieces would look all choppy without being as strong. So after it was made to the right length Ryan cut the end, aligned and tack welded the rail in place on the cross beam.

The lateral placement of the rails is now correct and they won't need to be "scalloped" for more tire room, like the previous frame rails. These have more than an inch of extra clearance inboard to the existing existing rear wheels and 345mm Hoosiers. And if you look above you will see two different lower control arm mounts on the cross beam - the first pair had a single mounting hole, but the final pair allow some adjustment so they were made with 3 mounting holes.

While planning the pick-up points and arm lengths it was determined that the existing lower rear control arms could stay untouched but the upper control arm (below left) was too short by several inches. New material was ordered and a longer upper arm, a new upper mount and a new upper crossmember were added (below right) to get the geometry where we wanted.